The invention relates to the treatment of gas streams. In another aspect the invention relates to treating an acid gas stream with an alkanolamine solution. In yet another aspect, the invention relates to selectively regenerating alkanolamine solution which has been contacted with acid gases.
The use of amines for the removal of hydrogen sulfide and carbon dioxide from gas streams is well known. Triethanol amine (TEA) was the first of the ethanol amines to become commercially available. It was used in the early gas treating plants. This amine has generally been displaced in gas treating plants by diethanol amine (DEA) and monoethanol amine (MEA). The advantage to the use of DEA and MEA lies in their lower molecular weights and their ability to more completely absorb hydrogen sulfide from the gas. Of these three amines, monoethanol amine is generally preferred because of its ability to produce sweet gas streams with extremely low hydrogen sulfide levels under the same operating conditions.
Frequently, large quantities of carbon dioxide occur in gas streams containing hydrogen sulfide. When complete hydrogen sulfide removal is attained, processes utilizing MEA and DEA also absorb essentially all of the carbon dioxide. There are frequent occasions when it would be desirable to send a major portion of the carbon dioxide with the treated gas stream while removing essentially all of the hydrogen sulfide. The current need for processes to selectively remove hydrogen sulfide from gas streams can be summarized as follows:
(1) The high cost of energy required to regenerate the amine solution can be reduced if less carbon dioxide is absorbed.
(2) The Claus process requires a high ratio of hydrogen sulfide to carbon dioxide for most economic operation, otherwise capital and operating costs for a Claus plant could soar.
(3) As environmental restrictions become more stringent, many of the low hydrogen sulfide to carbon dioxide streams now being flared will have to be treated before flaring.
(4) Synthetic natural gas streams are very high in carbon dioxide and must be de-sulfurized before feeding to any known catalytic conversion process to produce high BTU fuel.